This invention relates to a technique for protecting a coastal land from a rise in the sea level due to global warming by building a dam having pump-turbines along the coastline. More specifically, the invention relates to a technique for building a tidal water power plant by constructing a pond that separates the coastline from the offshore sea along the coastline, and by keeping the water level of the pond lower than the water level of the offshore sea. The inner pond functions as a lower pond and the offshore sea functions as an upper pond, whereby the environment is protected, and at the same time, tidal energy is developed.
As discussed at the International Symposium for Protecting Global Warming Phenomena held in Kyoto on December 1997, the problem of rising sea level is expected in the next century. Known techniques for protecting a coastal land from a rise in the sea level had been to increase the bulk and height of a levee or barrier. The inventor of the present invention has found that the technique for building a tidal power generation system operated during high tide in a bay, which was disclosed in Japanese Patent Application No. H9-200818 by the same inventor as the present invention, can be applied to protect the coast line from a rise of the surface of the sea, and that the tidal water generation system can be constructed at any coastline on the earth.
In H9-200818, in order to convert the tidal range in a bay into energy, a tidal channel is built on one side of or in the center of the bay, so that the channel extends from the bay entrance to the depth of the bay. The tidal range is kept in the natural state. Then, a multiplicity of rectangular ponds, with the coastline as one side of each rectangle, are constructed on one side or both sides of the channel. Each pond is surrounded by a dam, which includes one or more pump-turbines therein. To generate electric power during a high tide, the water level of each pond must always be kept lower than the average sea level. To be more precise, during nighttime and low tide, the pumps are driven to lower the water level of each pond, using excess electric power supplied from the power network. Then, during daytime and high tide, the seawater is introduced in each pond by the turbines until the water level of the pond reaches the preset level. This system can achieve at least 100% efficiency of pumped storage power generation. In order to construct this system economically, a single pond is first constructed as a unit. Then, after the construction of the first pond is completed, the next pond is constructed adjacent to the first pond, while the first pond is used to generate electric power. In this manner, all ponds can be successively constructed in due course.
If the sea level rises by 50 cm to 100 cm in the 21st century, it is inevitable that the coastline will recede. Such situation will cause decrease of the shore, elimination of the beach, and submergence of zero-meter areas. These problems will be especially serious in The Netherlands, Bangladesh, and islands with altitude of 1 meter. The present invention is an improvement of the above-mentioned invention of H9-200818, and is intended to allow the previous invention to be applied not only to the tidal power generation sites in a limited area, but also to any shore on the earth.
A coastal land, which is to be protected from a rise in the sea level, is separated from the offshore sea by constructing an offshore dam that extends in parallel with the coastline of the land. Partition dams extend from the both ends of the coastline to the offshore dam so as to be substantially perpendicular to the offshore dam. The partition dams and the offshore dam define a pond. The maximum water level of the pond is kept to a preset level which is lower than the average sea level of the offshore sea by several meters (e.g., 3 meters). This arrangement allows the coastline to advance toward the sea, instead of receding of the coastline. Caissons which contains pump-turbines are coupled with the offshore dam in order to achieve substantially 100% efficiency of tidal power generation, making use of the water-level difference between the offshore sea and the pond. This system also allows a composite energy of the tidal energy and the pumped storage power generation to be developed. Thus, the present invention aims to produce a new and clean energy, while reducing the driving energy, as well as to protect the coastal land from the rising the sea level and increase the area of the shore. The invention also aims to contribute to the prevention of global warming phenomena. A significant feature of the present invention over the previous one disclosed in H9-200818 is that the water level of each pond is controlled so as to be lower than the average sea level by 3 to 4 meters. This feature essentially allows propeller turbines to be used in any shore on the earth because the typical tidal range is about 2 meters at most shores, which is insufficient to allow the propeller turbines to output power.